1) Field Of The Invention
The present invention relates to oriented polymeric film coated on at least one side with an aqueous based polyethyleneimine primer coating composition. In particular, the present invention concerns oriented polymeric film coated in-line with an aqueous based polyethyleneimine, which renders the film more receptive to direct extrusion coating with other polymer layers, and to ink adhesion.
2) Prior Art
Oriented polymeric film, and particularly biaxially oriented polyethylene terephthalate (PET) film, has been widely used in packaging materials, magnetic tape applications, glazing applications, and reprographic film applications. It has good optical clarity and toughness which renders the film extremely suitable for these applications.
A major use of polymeric film is in lamination with other polymers. Often polyester film is extrusion coated with polyethylene, for example, to provide heat sealing or other properties not possible with polyester alone. Unfortunately, unprimed polymeric film is not very receptive to extrusion coating with other polymers. Most polymeric film is substantially inert and adhesion between the unprimed polymeric film and other extrusion coated polymers is poor.
Numerous primer coatings are known in the field for application to polymeric film to improve the adhesion of the film to various polymeric materials. Examples of such coatings include compositions based on vinylidene chloride polymers (U.S. Pat. No. 2,698,240), thermosetting acrylic or methacrylic polymers (U.S. Pat. No. 4,571,363), and like materials. Certain water dispersible copolyesters have also been disclosed as adhesives for laminating sheets of polyester film to one another or to sheets of nylon film as taught in U.S. Pat. Nos. 3,563,942 and 3,779,993. Corona discharge treatment is also used with and without such primer coatings to achieve adhesion between the polymeric film and the extruded polymer layer.
In common practice, polyethyleneimine is used as an adhesive coating between various polymeric films, such as polypropylene film and other polymers as taught by U.S. Pat. No. 4,139,643 to Hix et al. The use of polyethyleneimine as an adhesive between cellophane and polyethylene is known from Reissue Patent No. 28,554 issued to Curler et al. Coating polyester film with polyethyleneimine by a converter for adhesion to extruded polyethylene is generally known. However, it is known that the polyethyleneimine bond deteriorates rapidly to an unacceptable level under humid conditions. Thus, a converter will only employ polyethyleneimine, as a primer coating, when the laminate will not be exposed to prolonged humid conditions. These and other prior art applications for coating various polymeric films with polyethyleneimine are all performed by a converter rather than a film manufacturer.
In common practice for extrusion coating, a converter will corona treat polymeric film as received from the film manufacturer, coat the corona treated film with polyethyleneimine, and then extrusion coat another polymer onto the film to form a laminate. This operation in which the polyethyleneimine is coated by a converter is called "off-line" coating. For a converter to off-line coat polymeric film with polyethyleneimine requires expensive equipment. For example, a converter would need equipment to unwind the film, corona treat it, primer coat it, dry the primer coating, extrusion coat the primed film, cool the formed laminate, and rewind the film into a roll. In addition to equipment requirements, an off-line coating operation is time intensive for a converter.
Because of the above difficulties, it would be advantageous for a converter to obtain a ready-to-use treated and primed film, such that the primed film would be directly extrusion coatable without additional primer coating or corona treatment. In other words, it would be advantageous to the converter to receive a film from the manufacturer that merely required the converter to directly extrusion coat the desired polymeric material thereon to form a polymeric laminate.
A directly extrusion coatable polyester film is disclosed in U.S. Pat. No. 4,410,600 to P. T. McGrail. Disclosed is a biaxially oriented PET film coated "in-line" with a crosslinked styrene-maleic anhydride copolymer. The coated film, however, still requires corona treatment prior to extrusion coating by a converter. Coating polymeric film with a primer coating during the manufacturing process (before heat setting the film) is referred to as "in-line" coating.
None of the prior references addresses the problem of acceptable direct extrusion coatability of polymeric film, without additional primers or additional corona treatment. Moreover, none of the prior references discloses coating polyethyleneimine in-line rather than off-line as is conventionally known.
Accordingly, it is an object of this invention to provide an oriented, polymeric film which can be directly extrusion coated with other polymers, without the need for an additional primer coating or additional corona treatment, and can withstand prolonged humid conditions.
It is also an object of this invention to provide a polymeric film having a polyethyleneimine primer coating thereon in which the coating is applied in-line.
Additionally, it is an object of this invention to provide a polymeric film, in-line coated with an effective amount of polyethyleneimine, to improve ink adhesion.